Some of the major considerations in underground mining techniques are the methods and associated apparatus used to transport newly mined material from its natural location to a destination outside of the mine. All mining systems progress, and transport systems must be able to keep up with that progression. Generally speaking, such transport systems can include vehicles which can move independently of other machinery, vehicles which move in combination with other machinery (e.g. rail cars), and various types of conveyor systems.
In addition to the obvious reason for transporting material out of a mine--i.e. the desire to obtain ore--there are other productivity reasons for moving freshly mined ore as efficiently as possible. In particular, where freshly mined ore is allowed to accumulate within the mine, it obstructs, and in some cases prevents, the movement of mining machinery within the mine so that further extraction of fresh ore cannot take place until the already mined ore is moved out of the mine. Accordingly, movement of newly mined ore within a mine is an important productivity consideration in any mining system.
As new mining machines have been developed, and indeed as future generations of such machines are expected to develop, the need to efficiently move newly mined ore becomes more acute as the mining machines become more productive. If the systems for removing mined out ore from the mining location do not proceed on a rate comparable to the mining itself, the removal systems become the limiting factor in determining how fast ore can be removed from the mine. In short, improvements in the mining techniques and productivity are essentially worthless if their increased productivity is quenched by a lack of comparably increased productivity in the removal systems. Stated differently, at some point mining machine productivity becomes limited by haulage capacity, and if haulage capacity remains constant or decreases, the increase in mining machine productivity becomes essentially meaningless.
Accordingly, an ideal solution to the haulage problem would be some sort of continuous conveyor system in which the ore from the mining machine can be placed directly upon a conveyor and continue on that conveyor, or an appropriate system of conveyors, until it exits the mine. As would be expected, however, as mining proceeds, the various conveyors must be moved to keep up with the mining and the other associated transport systems. There thus exists a need in mining systems for conveyor belts, the length of which can be changed as mining proceeds.
One typical solution is known as a belt storage unit. A typical belt storage unit includes one end which is disposed near the mining or transport activity and another end which is disposed somewhat closer to the exit portion of the mine. Typically, a belt storage unit contains two stacks of return idlers with the excess belt material weaving back and forth between the stacked idlers. One or both of the stacks of return idlers are movable under electrical or hydraulic power so as to absorb or release conveyor belt material as the innermost end or "tailpiece" of the conveyor moves. Typically, however, the majority of belt storage units can only extend or retract in an unloaded condition, and perhaps more importantly, are not designed to operate in both directions; i.e. belt storage units usually can allow the panel belt to be retracted, but don't normally allow it to be extended. Furthermore, such extensible panel belts follow a rather complex series of movements and generally cannot operate when loaded with ore. Also, the number of idlers in the stacks, and the resulting amount of conveyor material which can be stored, is limited by the height of the mining tunnel, such tunnels typically having relatively limited vertical space.
Finally, the belts on conventional belt storage units generally must be moving in order for the belts to be extended, because the motors used to drive the belts typically lack sufficient horsepower to overcome friction when the belts are stationary. In other words, such units must be moving, but empty, in order to be adjusted.
Some other present techniques for dealing with the need to change the length of mining conveyors use carrier vehicles which support added supplies of belting material so that the belting material can be carried to the panel belt of a mine and then added in place. In yet other techniques, one or more cables are suspended between the tail and anchoring portions of a conveyor belt with a drum of belting material being carried on the cable so that as the suspended drum is pulled on the cables toward the anchor units, it retracts the belt. Other systems use movable "inby" (the innermost end of a conveyor, and where it is first loaded) and tail sections with movable supports in between for changing the length of a conveyor in a mining system.
All of these devices, however, require electrical or hydraulic power, most can only operate by either extending or retracting the length of the conveyor, but not both, and few have the capability to have their length either extended or retracted while they are both loaded and in conveying operation.
Accordingly, it is an object of the invention to provide a conveyor system which is extensible and retractable while loaded and while either operating or idle and which does not require its own power system, but which is passively extendable and retractable so that it can be extended and retracted using existing machinery in a mine to move it in the intended and desired direction.